Fiber optic faceplate liquid crystal display

ABSTRACT

In accordance with the teachings of this invention, a novel liquid crystal display is taught which includes a layer of liquid crystal material, a thin transparent layer, one or more polarizers, and a fiber optic faceplate. The fiber optic faceplate serves to allow ambient light from a much wider range of incident angles to illuminate the LCD than would be the case with prior art LCDs, and allows the viewer to position himself so as to avoid front surface glare and still see the display brightly illuminated, even in difficult lighting situations.

RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 07/462,679 filed Jan. 9, 1990, now U.S. Pat. No. 5,035,490.

TECHNICAL FIELD

This invention relates generally to liquid crystal display (LCD)systems, and particularly to LCD systems augmented with a specializedfiber optic faceplate enhanced with means for polarizing ambient lightpassing through the faceplate toward and away from a surface of the LCDsystem.

BACKGROUND

Typical prior art flat panel liquid crystal display systems aredescribed in "Flat-Panel Displays Come on Strong in Speed, Resolutionand Color," Computer Design, Feb. 1, 1989, pages 65 through 82.Operation and performance of direct multiplexed liquid crystal displays,including the twisted nematic (TN), the supertwisted birefringenceeffect (SBE), and the surface-stabilized ferroelectric liquid-crystal(SSFLC) display, are described by Scheffer "Direct-MultiplexLiquid-Crystal Displays," Seminar 4, Society for Information Display(SID) International Symposium Seminar Lecture Notes, Vol. 1, May 11,1987, pages 4.1 through 4.34. U.S. Pat. Nos. 2,400,877; 2,481,380, and2,544,659, issued to J. F. Dreyer pertain to the use of an alignedorganic dye as a polarizer.

It is known in the art to combine fiber optic faceplates with LCDsystems. An example of such a combination relevant to this presentinvention is described in U.S. Pat. No. 4,349,817 to Hoffman et al.(Hoffman), which patent is hereby incorporated by reference into thepresent case. Major advantages of LCDs include their compact, ruggedconstruction and their portability as display screens for portablepersonal computers.

Generally, LCDs which are intended for use in portable systems are ofthe reflection type in order to make use of available ambient light forillumination rather than incurring the weight, bulk, and powerconsumption characteristic of active backlighting. Such displays includea liquid crystal layer which is sandwiched between transparent front andback electrodes, and a specular or semi-specular (i.e., mirror-like)surface placed behind the display to enhance reflection. The system hasan off-state, i.e., no voltage is applied between the front and backelectrodes, and an on-state, i.e., such a voltage is applied.

The Hoffman patent pertains exclusively to LCDs of the dynamicscattering type. When this type of LCD is in the off-state the liquidcrystal is clear, permitting light to pass through and be reflected backout by the reflective back electrode. In the on-state the liquid crystalscatters light increasingly in proportion to increasing applied voltage.This mode of controlling the light transmissivity of the liquid crystalmaterial in response to the applied voltage is called the "dynamicscatter mode" (when light is transmitted through the LCD) and the"reflective dynamic scatter mode" (when light is reflected out the sameside of the LCD).

A major problem with the reflective dynamic scatter mode LCD device usedfor direct viewing is that of contrast, defined here as the brightnessratio of the on-state to the off-state. The problem with this particularart, then, is how to reduce excessive levels of incident light emanatingfrom unwanted light sources which are positioned outside the viewingangle of the LCD screen. Contrast desirably increases if these unwantedlight sources can be neutralized.

To solve this contrast problem resulting from stray light, Hoffmancoupled a specially designed fiber optic faceplate to a LCD system. Todescribe Hoffman's approach and the state of the prior art, applicantsinclude FIG. 1 and FIG. 2, labelled as Prior Art in the present case.These figures plus the discussion below paraphrase the disclosuressurrounding Hoffman's respective FIGS. 3 and 2.

FIG. 1 (Prior Art) shows a direct view liquid crystal image displaysystem 20 viewed directly under ambient light from a source of light 22such as a bright sky or brightly lit room (not shown). Light rays 24,25, and 26 from light source 22 hit a fiber optic faceplate 28 within anacceptance cone Theta_(max) [herein, T(max)] of faceplate 28. Rays 24,25, 26 are transmitted to a liquid crystal layer 30 of a liquid crystaldisplay device 31 over which faceplate 28 lies.

The definition and significance of the acceptance angle T(max) appearsin the discussion about Equation (1) below. T(max) is measured withrespect to an axis 27 which is parallel to the horizontallight-propagating axis (not labelled) of the optical fibers comprisingfiber optic faceplate 28 and perpendicular to the face of faceplate 28.

First considering the off-state condition, ray 24 hitting a localizedliquid crystal area 32 when in the off-state is specularly reflectedalong a ray path 34 to the eye 36 of an observer (not shown) who as aresult sees a bright display region.

Conversely, now considering the on-state condition, previously mentionedlight ray 26 hits a localized liquid crystal area 38 which is in theon-state, with the result that ray 26 is scattered so that only aportion of ray 26 is reflected. That is, the reflected portion of thescattered light follows a path 40, 42, 44, 46, and 48 back to observereye 36, which thus sees a relatively dark display region 38 (i.e.,on-state region 38).

To address stray light coming from other light sources such as thosepositioned as are light sources 50, 52, and 54 (our Sun), existingtechnology configures system 20 so that light enters and leavesfaceplate 28 only within a well defined faceplate 28 acceptance angleT(max). By this approach, stray light is absorbed by faceplate 28.

That is, by absorbing light from sources outside the acceptance coneT(max) of faceplate 28, such as a ray 56 from the Sun 54 and a ray 58from light source 52, faceplate 28 prevents undesirable loss of imagecontrast of the LCD images with respect to ambient light generated bysuch light sources as 22, 50, 52, and 54.

FIG. 2 (Prior Art) illustrates in cross-section a single optical fiber60 of the type bundled together to make up faceplate 28 shown in FIG. 1.Faceplate 28 is formed with many parallel optical fibers 60 which arefused together. Each fiber 60 has a light-transparent core 62 having anindex of refraction n₁, covered with a light-transparent sheath 64having an index of refraction n₂ which is less than n₁, which in turn iscovered with an optically absorbing material 66.

Faceplate 28 has an acceptance cone of angle T(max), an angle related tothe index of refraction=n₁ of core 62 with respect to the index ofrefraction=n₂ of sheath 64. These attributes are related according tothe well-known relationship expressed in Equation (1) below:

    sin T.sub.max =[(n.sub.1)2-(n.sub.2)2].sup.1/2 =N.A.       (1)

where N.A.=the Numerical Aperature of the optical fiber.

An incident light ray 25 falling within the acceptance angle T(max) tooptical fiber axis 27 propagates through core 62 by the well knownphenomenon of multiple total internal reflections from a boundary 70existing between core 62 and sheath 64. Conversely, an incident lightray 58 falling outside incidence angle T(max) will not be totallyreflected, but instead will propagate through boundary 70 intotransparent sheath 64, finally to be absorbed by light absorbing layeror material 66.

More simply stated, the function of the fiber plate in the Hoffman LCDis to absorb all light which strikes the display outside the viewingangle of the display (defined as the angle over which the displayprovides an image of acceptable contrast), thereby reducing stray lightand enhancing the contrast of the display. Even with this enhancement,however, the dynamic scattering type of LCD has not become acommercially important device due to its relatively limited viewingangle and poor contrast.

Twisted nematic (TN) and super twisted nematic (STN) LCDs, on the otherhand, have become commercially important in the last 10 or so yearslargely because they offer improved contrast and viewing angle comparedto previous types, such as the dynamic scattering LCD with or withoutthe Hoffman improvements.

Limited contrast and viewing angle, however, remain among the mostserious shortcomings of TN and STN LCDs, improved in these areas thoughthey may be. The LCD industry, in fact, continues to seek displayscapable of delivering the general appearance of printed characters onpaper.

Application of the teachings of Hoffman will not improve, and in factwill seriously degrade, the contrast of a TN or STN LCD. This is for tworeasons:

First, eliminating light which strikes the display at angles to thedisplay surface normal greater than the viewing angle of the displaywill not enhance the contrast because TN and STN displays depend uponthe action of polarizers on polarized light propagating within thedisplay rather than scattering to produce the light and dark areas oftheir images.

Second, introduction of a fiber plate, as taught by Hoffman, innear-contact with the liquid crystal layer itself will seriously reducethe image contrast because light passing through such a fiber plate isstrongly depolarized, thus largely destroying the distinction betweenthe light and dark areas of the image.

Additionally, it is neither necessary nor desirable to incorporate ameans, such as the Hoffman style fiber plate, which absorbs all lightoutside of the nominal viewing angle of the display into a TN or STNLCD.

The black interstitial material in the Hoffman fiber plate causes asharp transition from a normal display appearance to a completely blackdisplay appearance with increasing angle, which can be annoying to theviewer of a TN or STN type LCD. This is because the contrast of TN andSTN LCDs degrades slowly with angle, and, although viewing contrast maynot be fully acceptable at high angles, a viewer may be able todetermine the general nature of what is being displayed or merely thatsomething is being displayed, even when he views the display at highangles.

Since this information is frequently important or desirable to theviewer, the Hoffman style fiber plate does not constitute an improvementto many modern types of LCDs.

Hoffman teaches the application of a fiber plate composed of fibers eachhaving as low numerical aperture as possible and restricting the viewingangle by means of the black interstitial material as much as possible inorder to reject as much stray light as possible. In contrast, thepresent invention teaches the application of fiber plates having as higha numerical aperture as possible and permitting as wide a viewing angleas possible in order to gather as much ambient light as possible toilluminate the display.

FIG. 3 shows a typical prior art reflective liquid crystal displayutilizing polarizers. LCD 300 includes a layer of liquid crystalmaterial 301 sandwiched between drive matrices 302a and 302b forapplying electric fields to appropriate locations within the layer ofliquid crystal material 301. For example, selected pixel 304 (shown asdark, but may actually appear dark or light depending upon polarizerorientation) is shown within the layer of liquid crystal material 301,caused by an appropriate electric field in that location applied acrossthat portion of liquid crystal material 301 by matrices 302a and 302b.

Glass plates 303a and 303b serve to support drive matrices 302a and302b. On the other sides of glass plates 303a and 303b are formedpolarizers 305a and 305b, respectively. Polarizer 305a serves as theexposed surface of liquid crystal display 300, and polarizer 305b facessemi-diffused mirror 307, separated from polarizer 305b by gap 306 whichmay be conveniently filled up by a glass plate. If desired, mirror 307is formed as an aluminized coating on the surface of polarizer 305bwhich is not in contact with glass plate 303b.

One of the disadvantages of the prior art liquid crystal display 300 ofFIG. 3 is that, since glass plate 303b is generally rather thickcompared with the pixel-to-pixel spacing, and since mirror 307 isspecular or semi-specular in nature, a ghost image or "shadow" 310 isformed below the actual pixel 304. A simple construction of the paths oftwo light rays according to well-known principles of geometrical opticssuffices to show that this is true. Consider ray 308-1 which enters thedisplay from above on the left, traverses the display cell, is reflectedby mirror 307, and reemerges from the display as ray 308-2. Consideralso ray 309-1 which enters from above on the right and reemerges in asimilar manner as ray 309-2. Extensions of rays 308-2 and 309-2 cross at310, and hence appear to an observer to have come from 310. Also, sinceboth rays pass through the location of the selected pixel 304, theintensity of both rays is modulated by the action of the display to bethe same as that of the selected pixel 304. Ghost image 310 is thus avirtual image in the geometrical optics sense of the selected pixel 304lying behind 304 and, depending upon the observer's viewing position,may appear laterally displaced from 304 as well due to viewing parallax.

An additional disadvantage of prior art liquid crystal displays such as300 in FIG. 3 is that the apparent illumination of the display is astrong function of viewing angle, and that the display appears moststrongly illuminated by ambient light when viewed at an angle close tothat at which light also specularly reflects from the top displaysurface (the top surface of polarizer 305a in FIG. 3). The viewer isthus frequently tempted to view the display in a manner which causes himto have to contend with annoying glare.

SUMMARY OF THE INVENTION

In accordance with the teachings of this invention, a novel liquidcrystal display is taught which includes a layer of liquid crystalmaterial, one or more polarizers, and a fiber optic faceplate. The fiberoptic faceplate serves to allow ambient light from a much wider range ofincident angles to illuminate the LCD than would be the case with priorart LCDs, and allows the viewer to position himself so as to avoid frontsurface glare and still see the display brightly illuminated, even indifficult lighting situations.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts the operation of a prior art liquid crystal display,without polarizers, but using a fiber optic faceplate;

FIG. 2 depicts the operation of a fiber contained within a fiber opticfaceplate of FIG. 1;

FIG. 3 depicts a prior art liquid crystal display utilizing polarizers,and the ghost image formed therewith;

FIGS. 4a through 4c depict the liquid crystal display of FIG. 3, and theangle over which incident light may serve to illuminate the LCD;

FIGS. 5a through 5c depict the operation of a single fiber used in thefiber faceplate of the present invention;

FIGS. 6a through 6c depict the operation of one embodiment of an LCDdisplay constructed in accordance with the teachings of this invention,and the range of angles over which ambient light serves to illuminatethe LCD;

FIG. 7 depicts one embodiment of an LCD constructed in accordance withthe teachings of this invention and the elimination of the ghost imageobtained therewith; and

FIG. 8 depicts an alternative embodiment of an LCD constructed inaccordance with the teachings of this invention.

The example figures presented illustrate but one of the many possibleconstructions that can made according to invention defined by theclaims. These figures correspond to the example discussed below in theDetailed Description.

DETAILED DESCRIPTION OF THE INVENTION

The fiber faceplate LCD of this invention appears more brightlyilluminated than a conventional reflective LCD under a wide range ofambient lighting conditions due to the superior light diffusioncharacteristics of the fiber faceplate. To understand why this is thecase, consider a prior art reflective LCD shown in FIG. 4a (in which thedrive electrode and alignment layers, well known in the art, are omittedfor clarity).

The apparent background illumination is reflected ambient light.Consider a ray of ambient light entering the conventional display at A.After passing through the display cell, the ray emerges at B and is thenreflected by a semi-diffuse mirror at C. After reflection the lightpresent in the original ray is spread over a cone with half-angle φ dueto the diffusing action of mirror 307. This is shown in thetwo-dimensional polar plot of reflectivity of FIG. 4b, and thethree-dimensional polar plot of reflectivity of FIG. 4c. The axis ofthis cone is coincident with the ray C-D which emerges from the displayat the same angle as would the incident ray A-C, were the reflectionpurely specular in nature. That is, the cone describing the intensity ofthe reflected illumination as a function of angle is an article ofrevolution about the direction of specular reflection. This means thatonly light sources within the angle of reflecting off of the top surfaceof polarizer 305a, which is parallel to mirror 307, and directly back ina viewer's eyes will contribute significantly to the apparent backgroundillumination. Thus, unless the angle φ is large, only a relative few ofthe typical multiplicity of ambient light sources can contributeillumination. Due to the nature of the diffuse scattering process,however, light scattered at large angles tends to be depolarized. Thelight exiting the cell at B has been polarized by the action of the LCcell. If it is depolarized upon reflection at C by a strongly diffusingreflector (which would be necessary in order to produce a large angleφ), up to half of it will be absorbed by the LC cell polarizers 305a,305b, thus decreasing the display's apparent brightness. A large amountof diffusion and overall display brightness thus trade off against eachother, and this tends to restrict real displays to small values of φ. Asa consequence, the apparent illumination of conventional reflective LCDsis a strong function of angle and light sources which contribute to thatillumination must be located near a position that would cause anyspecular reflection (perhaps off of the front of the display) to fall inthe viewer's eyes. This restriction, coupled with the fact that theviewing angle over which the LC cell itself presents an image ofreasonable contrast may also be quite restricted, can have a disastrouseffect on image quality.

In order to understand the analogous action of the present inventionutilizing a fiber faceplate LCD, consider first the action of a singlefiber on incoming light as shown in FIGS. 5a-5c of the accompanyingfigures. In the top view of a fiber (FIG. 5a), one can see that onlythat portion of the light 501 entering the top which lies in a medianplane (i.e., a plane which includes the axis of the fiber; the rayentering at A lies in such a plane) will remain in that plane as itrattles down through the fiber and exits at the bottom. Other portionsof the light, such as the ray incident at B, will be deviated in theazimuthal direction at each reflection and will, upon exiting as lightbeam 511 at C, have accumulated some net azimuthal deviation relative tothe original direction of the incident, Ψ. All of the rays, incident atthe same angle, theta, with respect to the axis of the fiber, will alsoexit at the angle e with respect to the axis of the fiber.

There will be rays, however, among the multiplicity of rays whichdescribe the light filling the fiber which exit at every possibleazimuth Ψ. Light incident from a single direction is thus converted intoa hollow cone of light whose apex angle equals the incident angle, θ.FIG. 5b depicts a side view of the optical fiber of FIG. 5a, and FIG. 5cdepicts in three dimensions the operation of the optical fiber of FIGS.5a and 5b, showing that light incident from one direction is convertedinto a hollow cone of light having an apex angle equal to the incidentangle.

Consider now the embodiment of a fiber faceplate LCD of this inventionshown diagrammatically in FIG. 6a (again, with the drive electrode andalignment layers omitted for clarity). Incident illumination from asingle direction will be spread into a hollow cone by the action of theindividual fibers of fiber faceplate 619, as just described. Uponpassage through the LC cell it encounters specular reflector 607 whichsends it back through the cell without depolarization and the attendantloss in intensity. The second passage through the fiber faceplate 619results in a second azimuthal diffusion and the same hollow conical farfield pattern described above.

There are two key differences between this situation and that of theconventional reflective LCD, shown in two dimensions in FIG. 6b and inthree dimensions in FIG. 6c. First, since the diffusions take placeentirely before and entirely after the double passage of the lightthrough the LC cell and its polarizers 605a, 605b, there is no loss inlight due to depolarization. Second, the volume representing theintensity of light scattered at a given angle is now an article ofrevolution about the normal to the display surface, not about thedirection of specular reflection.

This means (a) that light from a given ambient source is spread over amuch larger far field angle than in the case of the conventionaldisplay, (b) that ambient light from a larger variety of directions cancontribute to the illumination apparent to a given viewer than in thecase of the conventional display, and (c) that the viewer need not beclose to a position which would cause specularly reflected light to fallin his eyes in order to see the display brightly illuminated.

FIG. 7 depicts one embodiment of a fiber faceplate LCD constructed inaccordance with the teachings of this invention, and how itsubstantially eliminates the ghost image.

Consider a geometrical construction with two entering rays, 701-1 and702-1, similar to that depicted in FIG. 3. In order to pass through theregion of selected pixel 304, rays 701-1 and 702-1 must enter the fiberplate directly above 304, due to the well-known light-conductingproperty of the individual fibers. Upon passing through the display celland reflecting off of mirror 607, reflected rays 701-2 and 702-2encounter the fiber plate a second time.

Because the thickness of the lower half of the display is typicallylarge compared with the fiber to fiber spacing in the fiber faceplate,rays 701-2 and 702-2 encounter entirely different fibers than did 701-1and 702-1 initially, and ray 701-2 encounters an entirely differentfiber than does ray 702-2. Also rays 701-2 and 702-2 strike the fibersthrough which they pass out of the display at random locations withinthe fibers' cores, depending upon the incident angles and azimuths(parameters θ and ψ in FIGS. 5a-c) of rays 701-1 and 702-1. Exiting rays701-3 and 702-3 are thus randomized in their exiting azimuths, asexplained previously in the descriptions of FIGS. 5a-c, and do not ingeneral appear to have come from a single region of space, i.e., a ghostimage.

The light which ordinarily would be concentrated in a ghost image issmeared out by the diffusing effect of a second passage through thefiber faceplate and now forms a much larger and more diffuse shadowsurrounding the selected pixel than in the case of the conventional LCDof FIG. 3. This larger and more diffuse shadow is less visible to theviewer than the ghost image of FIG. 3 in two ways. First, the shadow islargely intermixed with light which passed through nearby regions of thedisplay, and hence its maximum lightness or darkness, depending upon theoptical state of selected pixel 304, is not very different from that ofthe surrounding areas of the display. Second, the shadow issubstantially spatially diffused, like an out-of-focus image, and henceis not easily and clearly seen by the viewer as containing anyinformation.

The only way in which the viewer can observe the selected pixel clearlyis by means of the image 720, which exists at the top surface of thefiber faceplate due to the well-known light-piping properties of theindividual fibers in the faceplate. In order for this image to bespatially sharp, the thickness of polarizer 605a must be small comparedwith the size of a display pixel.

In one embodiment of this invention, polarizer 605a is formed of a thinlayer (typically within the range of approximately 0.5 to 100 micron) inorder to present a sharp viewable image 720 when used with typicaldisplay pixel spacings of 100 to 400 microns. Thin polarizer 605a can befabricated using an aligned organic dye, such as is described in theaforementioned Dreyer patents. In one specific embodiment, polarizer605a is fabricated using the 105MS polarizer coating available fromDa-Lite Screen Corporation of Cincinnati, Ohio. In some cases, anovercoating layer between the polarizer coating and the other functionallayers of the liquid crystal cell may be required, such as Da-LiteCorp's special polymer overcoating or a thin film overcoating of acompatible material such as silicon dioxide.

In an embodiment of this invention where polarizer 605b is used,polarizer 605b is formed in a similar manner as is polarizer 605a. Fiberfaceplate 619 can be fabricated to a thickness in the range ofapproximately 0.7 to 5.0 millimeters, preferably about 3.0 millimetershaving individual fibers in the range of, for example, 6 to 50 microns.In one embodiment, fiber faceplate 619 is made approximately of 0.66 naclear fused glass optical fiberplate available from Incom, Inc. ofSouthbridge, Mass.

FIG. 8 is a cross-sectional view depicting an alternative embodiment ofthis invention. LCD assembly 800 includes liquid crystal material 601sandwiched on each side by drive matrices 802a and 802b forming LCDelement 825, as is well known in the art. The rear side of LCD assembly800 includes rear glass layer 812 of any desired thickness, typically athickness within the range of approximately 0.7 to 5.0 mm, preferablyapproximately 3.0 mm. Rear polarizer/mirror 807 is used to both reflectlight and polarize light for passage through LCD material 601. Ifdesired, a separate polarizer and mirror is used, rather than combinedpolarizer/mirror 807. The front side of LCD assembly 800 includestransparent layer 810, of any desired thickness, for example within therange of approximately 50 to 200 microns, and preferably approximately100 microns or less. Polarizer layer 605a is formed thereon, and can beof conventional type and need not be a thin film layer or compatiblewith the manufacturing steps used to fabricate LCD element 825, aspolarization layer 605a is formed outside of LCD element 825 inaccordance with the embodiment of the present invention. Fiber faceplate619 is placed on polarizing layer 605a.

In the embodiment in FIG. 8, fiber faceplate 619 is placed at a distance(determined by the thickness of polarization layer 605a and thin glassplate 810) from LCD element 825. In accordance with this embodiment ofthe present invention, the gap between fiber faceplate 619 and liquidcrystal material 601 is allowed to be a finite distance and stillprovide a reasonable image to be delivered to the top surface of fiberfaceplate 619 for viewing by a user, and without the problems ofghosting experienced with prior art LCD displays. This gap, whichcomprises the collective thicknesses of layers 605a and 810, may bewithin the range of approximately 50 to 250 microns, preferably withinthe range of approximately 100 to 125 microns or less.

In accordance with the teachings of this invention, liquid crystaldisplay assembly 800 can be fabricated in any convenient manner. In oneembodiment, fiber faceplate 619, polarizer layer 605a, and thin glasslayer 810 are assembled together and then applied to liquid crystaldisplay 825.

In an alternative embodiment, LCD element 825 is fabricated in aconventional manner. Additional layers are then assembled in order toprovide LCD assembly 800 without fiber faceplate 619. Assembly 800 isthen cut to a desired size and shape, and fiber faceplate 619 is added.In accordance with the teachings of this embodiment, the fiber faceplate619 stock material can be manufactured to smaller planar dimensions thanthe LCD mother glass from which a plurality of LCD elements may be cut.In this embodiment, fiber faceplate 619 can be made to any desiredthickness without concern for adding difficulty in scribing, breaking,or sawing LCD assembly 800, as LCD elements are cut to size prior tomounting fiber faceplate 619 thereon. Increased thickness of fiberfaceplate 619 minimizes rainbowing in LCD 619.

Thus, in accordance with the teachings of this invention, a novel LCDstructure is taught including a fiber faceplate (a) which does notdegrade the viewing angle, contrast, and other operating features of theliquid crystal element itself, (b) which provides a wider angle overwhich ambient light is received for the purposes of illumination, and(c) which provides that the viewer need not be close to a position thatwould cause specularly reflected ambient light to fall in the viewer'seyes.

The teachings of this invention are useful not only for liquid crystaldisplays including polarizers on both sides of the liquid crystal, butalso those liquid crystal displays which include at least one polarizer,such as those liquid crystal displays which include a polarizer only onthe viewer side of the liquid crystal. The teachings of this inventionare also applicable to those liquid crystal displays which, in additionto one or more polarizers, also include one or more birefringentelements serving to convert light between elliptical polarization andlinear polarization.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference.

The preceding Detailed Description and Drawings provide several specificexamples of the best modes for practicing the claimed invention.However, it is the following claims that actually (a) define theinvention and (b) establish the scope of the invention.

The invention claimed is:
 1. A direct view image display apparatus,comprising:a) a reflecting liquid crystal display (LCD) device;i) formedfor operating in a nondynamic scattering mode; and ii) having an LCDsurface; b) a fiber optic faceplate;i) having an upper face and a lowerface; ii) positioned with the lower face facing the LCD surface; iii)having a multiplicity of straight and rigid optical fibers whoselongitudinal axes are parallel to each other and substantiallyperpendicular to;1) the upper face and the lower face of the faceplate;and 2) the LCD surface; iv) each of the fibers being formed to cooperatewith the reflective LCD surface to collect and project through thefaceplate any of a plurality of light rays emitted by an ambient lightsource if any, thereby enhancing the visibility of the image displayedon the upper face of the faceplate; c) a polarizer;i) positioned betweenthe LCD surface and the faceplate; and ii) formed for polarizing thelight passing between the LCD surface and the faceplate; and d) atransparent layer positioned between the LCD surface and thepolarizer;the polarizer and the transparent layer spacing said LCDdevice apart from the faceplate by a cap n, wherein n is sufficientlysmall to limit the optical fibers through which light rays from aparticular area of the LCD surface can be projected.
 2. An apparatus asin claim 1 wherein the polarizer comprises a polarizer having athickness with in the range of approximately 0.5 to 100 microns.
 3. Anapparatus as in claim 1 wherein the polarizer comprises an organic dye.4. An apparatus of claim 1 wherein the fiber optic faceplate is formedto a thickness within the range of approximately 0.7 to 5.0 millimeters.5. An apparatus as in claim 1 wherein the optical fibers comprisesglass.
 6. The apparatus defined in claim 1, further including:asheath:a) formed to enclose each of the fibers along its longitudinalaxis; b) formed to azimuthally diffuse within the faceplate the ambientlight if any incident on the faceplate thereby enhancing the visibilityof the image displayed on the upper face of the faceplate.
 7. Anapparatus as in claim 1 wherein the transparent layer has a thicknesswithin the range of approximately 50-200 microns.
 8. An apparatus as inclaim 1 wherein the transparent layer has a thickness of less thanapproximately 100 microns.
 9. A screen apparatus formed for displayingcharacters produced by a liquid crystal display (LCD) system capable ofoperating in the presence of an external light source, the apparatuscomprising:a) a faceplate;i) transparent to light; ii) having an outersurface and an inner surface, the two surfaces being aligned to begenerally coplanar; iii) formed by bundling an array of light tubes tobe simultaneously parallel to one another but perpendicular to both theouter surface and the inner surface; and iv) formed to transmit lightfrom the external light source to illuminate the characters; b) a firstmeans;i) formed for polarizing the light passing through the faceplate;and ii) positioned behind and substantially coplanar with the innersurface of the faceplate; c) a second means;i) formed for generating thecharacters with a liquid crystal display; ii) positioned behind andsubstantially coplanar with the inner surface of the faceplate; and iii)including a transparent layer positioned between said first means andthe said liquid crystal material of said liquid crystal display; and d)a third means;i) formed for specularly reflecting the light that passesthrough the faceplate; and ii) positioned behind and substantiallycoplanar with the inner surface of the faceplate, the first means andthe second means.
 10. An apparatus as in claim 9 wherein the first meanscomprises a polarizer having a thickness within the range ofapproximately 0.5 to 100 microns.
 11. An apparatus as in claim 9 whereinthe first means comprises a polarizer comprising an organic dye.
 12. Anapparatus of claim 9 wherein the faceplate is formed to a thicknesswithin the range of approximately 0.7 to 5.0 millimeters.
 13. Anapparatus as in claim 9 wherein the light tubes comprise glass.
 14. Anapparatus as in claim 9 wherein the light tubes have a numericalaperture of 0.66 or more.
 15. An apparatus as in claim 9 wherein thetransparent layer has a thickness within the range of approximately50-200 microns.
 16. An apparatus as in claim 9 wherein the transparentlayer has a thickness of less than approximately 100 microns.
 17. Avisual image display apparatus, comprising:a) a light reflective liquidcrystal display (LCD) device, the LCD device including a fronttransparent electrode layer and a front orientation layer; b) a fiberoptical faceplate through which light can pass, positioned in front ofthe LCD device; and c) a polarizer through which light can pass,positioned between said fiber optic faceplate and said LCD device; andd) a transparent layer positioned between said polarizer and said LCDdevice.
 18. An apparatus as in claim 17 wherein the transparent layerhas a thickness within the range of approximately 50-200 microns.
 19. Anapparatus as in claim 17 wherein the transparent layer has a thicknessof less than approximately 100 microns.
 20. A direct view image displayapparatus, comprising:a) a reflecting liquid crystal display (LCD)device;i) formed for operating in a nondynamic scattering mode; and ii)having an LCD surface; b) a fiber optic faceplate;i) having an upperface and a lower face; ii) positioned with the lower face facing the LCDsurface; iii) having a multiplicity of straight and rigid optical fiberswhose longitudinal axes are parallel to each other and substantiallyperpendicular to, said optical fibers having a numerical aperture of atleast 0.66;1) the upper face and the lower face of the faceplate; and 2)the LCD surface; iv) each of the fibers being formed to cooperate withthe reflective LCD surface to collect and project through the faceplateany of a plurality of light rays emitted by an ambient light source ifany, thereby enhancing the visibility of the image displayed on theupper face of the faceplate; c) a polarizer;i) positioned between theLCD surface and the faceplate; and ii) formed for polarizing the lightpassing between the LCD surface and the faceplate; and d) a transparentlayer positioned between the LCD surface and the polarizer.